In a semiconductor integrated circuit (LSI), a relatively small-type nonvolatile semiconductor memory device is required, which can be embedded together with other elements in a single chip and which is capable of retaining stored data even after a power supply is cut off. The embedded-type nonvolatile semiconductor memory devices are used for a various purposes such as providing redundancy for large-capacity memories including dynamic random access memories (DRAMs) and static random access memories (SRAMs), storing codes including cryptographic keys managing manufacturing history, or tuning analog circuits. Conventionally, laser fuses have been used as memory elements for nonvolatile semiconductor memory devices used for the above-mentioned purposes. A laser fuse needs a special fuse blowing apparatus and a process associated with the special fuse blowing apparatus. In addition, laser fuses are difficult to miniaturize. Using laser fuses results in increase in the proportion of the area occupied by each laser fuse in the chip. Such a problem of the higher occupancy of laser fuses encourages development of anti-fuse storage elements having a MOS structure, for example, to replace the laser fuses. An anti-fuse storage element is disclosed in Japanese Patent Application Publication No. 2008-171477.
In a memory that employs MOS-structure anti-fuse storage elements, an erroneous writing may occur in a MOS-structure anti-fuse storage element. Such a write an erroneous writing is a write disturb fault. To avoid occurrence of the write disturb fault, each memory cell is provided with two ports. Consequently, the number of elements and the number of signals increase in the memory cell. Such increases result in a problem that the memory cells occupy a larger area.